Is an invasive species ‘infecting’ Alaska’s waters?

The waters of Whiting Harbor near Sitka, Alaska, are icy this late winter morning, but “ROVer” doesn’t mind, it doesn’t even shiver. The remotely operated vehicle, or ROV, from NOAA’s Auke Bay Laboratories is on a mission: Find “rock vomit.”

Lesser known as Didemnum vexillum, rock vomit is an invasive sea squirt discovered in Alaska waters in June 2010. It was the first-confirmed occurrence of this tenacious species in the state.

Rock vomit is so named for its penchant for spreading over hard surfaces such as piers, ship hulls, large seashells and rocks. It feeds on the tiny plankton and decaying plant material it filters from seawater, and can be lethal to other creatures — including commercially important species of fish.

“It’s a crazy organism,” says Linda Shaw, a NOAA Fisheries habitat biologist. “It smothers other creatures while producing acidic toxins that in turn prevent anything from growing on it. Rock vomit creates a type of barrier between groundfish and their food. It’s been causing problems worldwide.”

If allowed to spread, rock vomit could pose a serious threat to Alaska’s mariculture business. Alaska mariculture, the farming of fish and aquatic plant in the open ocean or saltwater ponds and pools, is valued at about $500,000 a year. With further development, it could be worth as much as $100 million. The state’s commercial groundfish fisheries also stand to lose. That’s why state and federal agencies are working with other partners to battle the slimy squirt before it gains a foothold in Alaska’s pristine and productive waters.

To understand the extent of rock vomit’s distribution, divers from the Alaska Department of Fish and Game searched Sitka’s Whiting Harbor last fall and this past January. But, they could cover only so much seafloor: some areas are too deep for human divers.

It was time to pull out the big gun. In late February, staff from NOAA Fisheries Alaska Region and Alaska Fisheries Science Center turned to ROVer to complete the analysis.

“We couldn’t have done it without ROVer,” said Tammy Davis of ADF&G’s invasive species program. “Thanks to this cooperative effort with NOAA Fisheries, the data collected by ROV survey will complement ADF&G's dive surveys, giving us a more complete picture of what is really going on beneath the surface.”
Where ‘vomit’ is part of a day’s work

ROVer’s video camera “eyes” literally light up as the submersible descends beneath the sea surface in search of rock vomit. On the support vessel, four NOAA scientists work together to operate the ROV. David Csepp is at the helm, using remote control to power ROVer’s thrusters while Keith Cox navigates. Katharine Miller fires up her laptop that helps her track the vehicle. Linda Shaw, the invasive species specialist, guides the hunt. Like any big-shot explorer, ROVer has his own staff.

“EEEWWW …” A close-up of the sea squirt Didemnum vexillum, otherwise known as rock vomit. (Credit: Photo courtesy of Alaska Department of Fish and Game.)

ROVer is looking for mats of brownish goo covering the sea floor, rocks or even fronds of algae. ROVer’s team must pay close attention to what the underwater explorer highlights because there are native sea squirts, too. Who knows what discoveries might be made?
Awaiting the diagnosis

The mission nets a vast amount of video. Today, researchers are reviewing that footage to determine the range and distribution of the rock vomit. So far, preliminary results are encouraging.

“We can say that there are no big infestations outside the harbor,” said Shaw. “But there are some things we want to take a closer look at as we review the video.”

Once the analysis is complete, the next step will be for NOAA scientists to work with partner organizations, including the University of Alaska Southeast, Sitka Sound Science Center, AmeriCorps, Smithsonian Environmental Research Center, San Francisco State University, and Sitka Tribe of Alaska to evaluate how they might control – or eradicate altogether – the invasive organism with the off-putting name.
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